From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933565AbaIDBIY (ORCPT ); Wed, 3 Sep 2014 21:08:24 -0400 Received: from mail-pa0-f42.google.com ([209.85.220.42]:54869 "EHLO mail-pa0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933311AbaIDBIX (ORCPT ); Wed, 3 Sep 2014 21:08:23 -0400 Date: Wed, 3 Sep 2014 18:06:34 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@eggly.anvils To: Naoya Horiguchi cc: Andrew Morton , Hugh Dickins , David Rientjes , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Naoya Horiguchi Subject: Re: [PATCH v3 4/6] mm/hugetlb: add migration entry check in hugetlb_change_protection In-Reply-To: <1409276340-7054-5-git-send-email-n-horiguchi@ah.jp.nec.com> Message-ID: References: <1409276340-7054-1-git-send-email-n-horiguchi@ah.jp.nec.com> <1409276340-7054-5-git-send-email-n-horiguchi@ah.jp.nec.com> User-Agent: Alpine 2.11 (LSU 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 28 Aug 2014, Naoya Horiguchi wrote: > There is a race condition between hugepage migration and change_protection(), > where hugetlb_change_protection() doesn't care about migration entries and > wrongly overwrites them. That causes unexpected results like kernel crash. > > This patch adds is_hugetlb_entry_(migration|hwpoisoned) check in this > function to do proper actions. > > ChangeLog v3: > - handle migration entry correctly (instead of just skipping) > > Signed-off-by: Naoya Horiguchi > Cc: # [2.6.36+] 2.6.36+? For the hwpoisoned part of it, I suppose. Then you'd better mentioned the hwpoisoned case in the comment above. > --- > mm/hugetlb.c | 21 ++++++++++++++++++++- > 1 file changed, 20 insertions(+), 1 deletion(-) > > diff --git mmotm-2014-08-25-16-52.orig/mm/hugetlb.c mmotm-2014-08-25-16-52/mm/hugetlb.c > index 2aafe073cb06..1ed9df6def54 100644 > --- mmotm-2014-08-25-16-52.orig/mm/hugetlb.c > +++ mmotm-2014-08-25-16-52/mm/hugetlb.c > @@ -3362,7 +3362,26 @@ unsigned long hugetlb_change_protection(struct vm_area_struct *vma, > spin_unlock(ptl); > continue; > } > - if (!huge_pte_none(huge_ptep_get(ptep))) { > + pte = huge_ptep_get(ptep); > + if (unlikely(is_hugetlb_entry_hwpoisoned(pte))) { > + spin_unlock(ptl); > + continue; > + } > + if (unlikely(is_hugetlb_entry_migration(pte))) { > + swp_entry_t entry = pte_to_swp_entry(pte); > + > + if (is_write_migration_entry(entry)) { > + pte_t newpte; > + > + make_migration_entry_read(&entry); > + newpte = swp_entry_to_pte(entry); > + set_pte_at(mm, address, ptep, newpte); set_huge_pte_at. (As usual, I can't bear to see these is_hugetlb_entry_hwpoisoned and is_hugetlb_entry_migration examples go past without bleating about wanting to streamline them a little; but agreed last time to leave that to some later cleanup once all the stable backports are stable.) > + pages++; > + } > + spin_unlock(ptl); > + continue; > + } > + if (!huge_pte_none(pte)) { > pte = huge_ptep_get_and_clear(mm, address, ptep); > pte = pte_mkhuge(huge_pte_modify(pte, newprot)); > pte = arch_make_huge_pte(pte, vma, NULL, 0); > -- > 1.9.3